/// <summary>
        /// Preserves state associated with this page in case the application is suspended or the
        /// page is discarded from the navigation cache.  Values must conform to the serialization
        /// requirements of <see cref="SuspensionManager.SessionState"/>.
        /// </summary>
        /// <param name="sender">The source of the event; typically <see cref="NavigationHelper"/></param>
        /// <param name="e">Event data that provides an empty dictionary to be populated with
        /// serializable state.</param>
        private void NavigationHelper_SaveState(object sender, SaveStateEventArgs e)
        {
            try
            {
                SaveModel();

            }
            catch (Exception exc)
            {
                
                throw;
            }

        }
 /// <summary>
 /// Preserves state associated with this page in case the application is suspended or the
 /// page is discarded from the navigation cache.  Values must conform to the serialization
 /// requirements of <see cref="SuspensionManager.SessionState"/>.
 /// </summary>
 /// <param name="sender">The source of the event; typically <see cref="NavigationHelper"/></param>
 /// <param name="e">Event data that provides an empty dictionary to be populated with
 /// serializable state.</param>
 private void NavigationHelper_SaveState(object sender, SaveStateEventArgs e)
 {
     // TODO: Save the unique state of the page here.
 }